RYDBERG: PHYTOGEOGRAPHICAL NOTES 93 
but not so common in the Alps. It is the only species of the 
group there. It is, therefore, not probable that its ancestry came 
from that region. The group is represented in both North 
America and Asia by several species. The American species, 
except P. nivea and P. uniflora, are rather local, and are modified 
to adapt themselves to local conditions. Both P. nivea and P. 
uniflora as well as P. villosa (found in the northwestern corner of 
this continent) are found in Asia, together with several others of 
the group. P. nivea itself is common there in the mountains as 
well as in the arctic, while it has been collected only at a few 
places in the Rockies of Colorado. It is therefore probable that 
the group originated in Asia. 
Let us now discuss the plants of this category. The following 
plants are common to the arctic regions of both continents, the 
Alps, and the Rockies as far south as Colorado. Most of these are 
also found in Asia. Those with a star are also found in the 
subalpine regions. 
*Phleum alpinum Salix reticulata 
*Trisetum subspicatum Oxyria digyna 
*Deschampsia caespitosa *Bistorta vivipara 
Poa cenisia Silene acaulis 
*Poa alpina Thalictrum alpinum 
Festuca supina Ranunculus pygmaeus 
*Festuca ovina Draba fladnizensis 
* Festuca rubra Muscaria adscendens 
Juncus triglumis Potentilla nivea 
Juncus castaneus *A stragalus alpinus 
*Juncoides spicatum Campanula uniflora 
Lloydia serotina Myosotis alpesiris 
Some of these species extend into mountains situated so far 
south that they could not have been connected with the arctic 
regions even in the glacial times. The existence of these species 
there has to be explained in some other way. In most cases their 
seeds were probably carried by birds: or other animals or by 
the wind. Included among such plants are the following: 
Lloydia serotina, a typical arctic-alpine plant, is found not 
only in the arctic regions, the mountains of northern Europe and 
Asia, the Alps, the Rockies and the Sierra Nevada, but also in 
